Fluoride in various chemical forms and exposures has been repeatedly shown to have actions on bone matrix and on bone cells (osteoblasts and osteoclasts). The anabolic properties of fluoride were once explored for use in the treatment of postmenopausal osteoporosis. Excessive systemic fluoride can result in calcification of soft tissues (e.g. ligaments), osteosclerosis, osteoporosis, and osteomalacia which can compromise bone quality and strength leading to skeletal fluorosis. Despite a wealth of scientific literature a gap of knowledge exists in understanding the molecular mechanisms of fluoride actions on bone cells. We posit that genetic determinants that encode proteins and pathways involved in bone homeostasis underlie fluoride actions on bone cells and their hematopoietic precursors. Using extended phenotyping, we identified differences in osteoclastogenesis between inbred mouse strains, thus supporting the contribution of genetic background. The goal of the proposed studies, to identify fluoride responsive genetic loci in an animal model using a whole genome approach, will be pursued in the following Specific Aims: SpA1: Quantitative trait loci (QTL) mapping will be performed using C57BL/6J and C3H/HeJ inbred mice as progenitor strains in a two generation cross to produce a panel of F2 progeny. F2 mice will be treated with or without fluoride in their drinking water. Multiparameter phenotyping will be performed: serum biomarkers of bone formation/resorption; ex vivo osteoclastogenesis and osteoprogenitor assays; and ex vivo hematopoietic (CFC) assays will be performed. Additionally, selected bones will be phenotyped for BMD (microCT). A genome scan with an average SNP density of 3 Mb across the autosomes and 7 Mb across Chr. X will be performed followed by genetic analyses using a variety of interval mapping methods. SpA2: First determine fluoride response variation among a collection of domestic and wild type inbred mouse strains utilizing the phenotyping and fluoride treatment protocol above. Second, perform in silico mapping strategies. The broad and long term objectives are to identify and characterize fluoride responsive genetic variations, e.g. polymorphisms, in an animal model and later in humans. Public Health Significance: The goal of this project is to identify fluoride responsive chromosomal regions in an animal model. The long term goals are to characterize fluoride responsive genetic variations in an animal model, to identify those at risk populations who are susceptible to the unwanted or potentially adverse effects of fluoride action, and to elucidate fundamental mechanisms by which fluoride affects biomineralization. This animal studies project will generate interpretable and useful information relevant to public health issues like osteoporosis and skeletal fluorosis.